Not applicable.
Not applicable.
The present invention relates to swarf collecting apparatus and methods and more specifically to a method of controlling a swarf collecting conveyor to clear swarf obstructions which cause excessive conveyor motor and drive component loading.
Many industries routinely employ lathes, drills, mills and other machinery having specially configured cutting bits to shape metal work pieces by removing metal xe2x80x9cchipsxe2x80x9d therefrom. The chips which are removed come in many different shapes and sizes which are collectively referred to as swarf.
Many work piece shaping processes require a plurality of machines arranged at sequential work stations along a machine line. In these instances, after shaping at one station, a work piece is conveyed to a subsequent station for further shaping, each station generating swarf during the process.
To remove swarf from machine stations, often a conveyor belt is positioned below or adjacent a machine line to automatically catch flushed swarf and convey the swarf to a collection bin at the end of the belt. When the bin is full it is emptied or replaced with another bin. To facilitate use of large collection bins and thereby increase the time between emptying or replacement, most conveyors include a section which conveys upwardly at an inclined angle (e.g. 45 degrees) so that a belt end can be located above an elevated bin wall. To maintain swarf on the belt during inclined conveying (i.e. impede swarf from falling off lateral edges of the conveyor), a conveyor housing including a roof section is typically provided along the inclined section. Conveyor belts are particularly useful where the number of work stations and associated metal removing machines is large.
To cool work pieces and machine cutting tools and to flush swarf away from cutting bits during machining, a liquid coolant is typically dispersed at or near the cutting bits. In addition, swarf inside the bin or on the belt may be cooled by direct coolant dispersion thereon.
Swarf conveyor belts are typically driven by a motor capable of driving the belt in at least a forward direction. During machining, the belt is continuously driven to convey swarf from work stations.
Unfortunately swarf removing systems of the above kind can become obstructed by swarf during operation in at least two different ways. First, swarf can cause conveyor clogging. Only a certain swarf volume can pass though a conveyor housing at any time. Where swarf accumulates adjacent or within a housing, eventually, the accumulation can clog between the belt and housing impeding belt movement.
Second, swarf can become entangled between a belt and a stationary conveyor component (e.g. the housing) acting as a harness impeding belt movement. In this case, an elongated piece of swarf, typically a long corkscrew shaped shaving, can become ensnared at opposite ends between the belt and another component restricting belt movement.
In addition to damaging belt and other conveyor components, clogging and other forms of belt restriction caused by swarf (and or parts, bar ends, tools, etc.) increase motor load and, at some point, can damage motor components if the load becomes excessive.
One solution to belt obstructions has been to equip conveyors with manually operable motors capable of both forward and reverse operation. In this case, when swarf conditions cause motor overloading, an operator can stop the belt, reverse the belt, clear the obstruction and again restart the belt. Removing an obstruction is referred to herein as xe2x80x9cclearingxe2x80x9d.
Unfortunately, this solution to the problem has a number of shortcomings. First, this solution requires an operator to assist what is otherwise an automatic system for removing swarf from work stations. While the operator only needs to act after a clog or entanglement is detected, practically the operator must always be present to identify clogs and entanglements.
Second, where the time required to clear a belt is appreciable, an entire machine line may have to be shut down during the clearing process, further increasing costs associated with the system.
Third, if the obstruction is not noticed immediately, clogged swarf may cause belt, housing and/or motor damage prior to an operator stopping the belt.
Fourth, if the obstruction is not noticed immediately, swarf may accumulate upstream of the clog and fall from the belt. In addition, excessive cooling agent may be flushed into the belt system generally causing a mess or overflowing onto the floor.
Fifth, where the obstruction occurs inside the housing, it may be difficult for an operator to identify the obstruction until swarf backs up to the mouth of the housing.
Another solution for removing swarf obstructions is to provide an automatic clutch on the motor which allows the shaft which drives the belt to slip when motor load becomes excessive. In this case, instead of damaging motor and conveyor components, a clutch allows the motor to operate with a safe load and the belt stops until an operator can perform a clearing process to remove the obstruction.
While this solution reduces the possibility of motor and conveyor component damage, it to is encumbered with shortcomings. For example, this solution still requires an operator to be present to clear every obstruction that occurs. In addition, when the belt is stopped due to overloading, either the entire machine line must be shut down or swarf will continue to accumulate on the belt. Shutting down the entire line is costly. However, swarf accumulation can eventually exceed belt receiving capacity with excess swarf falling off the belt onto a floor surface. This is especially dangerous when swarf is extremely hot as is often the case with metal shavings or the like.
Moreover, as swarf accumulates on a stationary belt during clearing, the accumulated swarf causes conditions which will likely lead to further obstruction once the belt is again running in the forward direction.
One solution to the swarf jamming problem is described in U.S. patent application Ser. No. 09/081,538 entitled xe2x80x9cMethod and Apparatus for Controlling Conveyorxe2x80x9d filed on May 19, 1998. That application teaches a system wherein conveyor motor load is sensed and, when the load exceeds a predetermined load likely to correspond to a jam, the conveyor is stepped through a jam clearing process a specific number of times, the process and number of times calculated to likely clear the jam. For example, the clearing process may be to reverse the conveyor motor a given number of turns and then, once again, drive the motor in the forward direction. In the alternative the clearing process may be to reverse the conveyor until the conveyor has traveled in the reverse direction a specific distance and then, once again, drive the conveyor in the forward direction.
While this solution including counting the number of clearing processes is much better than prior solutions, under certain circumstances even this solution can be insufficient to protect the motor and conveyor components. For example, where each clearing process includes reversing the conveyor motor until a clearing process milestone is achieved prior to driving the motor in the forward direction, the milestone may never be reached if the jam also prohibits reverse conveyor travel. For example, where a clearing process requires 10 motor rotations prior to again driving the motor in the forward direction, if a jam impedes reverse conveyor travel, the 10 rotations are never achieved and the motor may either be damaged or destroyed. Similarly, if the milestone is a specific conveyor reverse travel distance, the reverse distance will never be achieved if reverse motion is impeded.
Moreover, even where a jam does not prohibit reverse motion, the jam may impede reverse motion such that reverse motion is slowed to the point where excessive load is placed on the motor.
In addition, even with a single machining process swarf characteristics may vary appreciably in ways that affect the optimum clearing protocol. For example, where swarf consists of relatively light weight pieces of metal, the torque required to drive the motor and conveyor in the reverse direction may be much smaller than the torque required to drive in reverse when swarf consists of relatively heavy metal pieces. Given a threshold total amount of motor work acceptable during a clearing process, the threshold is achieved with less clearing processes when the swarf includes heavy pieces and the load is large than with light weight pieces when the load is small. Thus, the optimum number of clearing processes where swarf pieces are light weight will often be greater than the optimum number when the pieces are large.
Furthermore, the likelihood of eliminating a jam via a clearing process is also related, in some respects, to swarf piece size. For example, On one hand where swarf pieces are relatively small jams that do occur will likely be relatively easy to eliminate as any jam will likely constitute a small swarf piece that can be dislodged relatively easily. On the other hand, where swarf pieces are relatively large jams that do occur will likely constitute swarf piece that are much larger and hence more difficult to move. With that said, it is likely that, given the same clearing process, it can be predicted that a small swarf jam would be easier to clear than a large swarf jam. For this reason the optimum number of clearing processes to be performed would also depend upon swarf size. A simple clearing process counting mechanism does not account for these differences.
Thus, a need exists for a system that will facilitate a clearing process when a conveyor jam occurs but that will protect the conveyor motor in the event that clearing process milestones cannot be achieved and that will cause an optimum clearing process independent of swarf characteristics.
The present inventor has recognized that all of the problems with the prior art systems described above can be address by providing a clearing procedure that is time based instead of being based on a specific number of completed clearing processes. To this end, when a jam is detected due to excessive motor load, the present invention requires that a clearing protocol including a series of clearing processes commence and that a timer begin timing the duration of the clearing protocol. When the timer reaches a specific threshold value calculated to likely clear any jam, the system aborts the protocol independent of the number of separate processes that were completed.
Thus, even if a jam prohibits reverse conveyor motion the present invention protects the conveyor motor from damage. Similarly, even where a jam impedes reverse motion the inventive system will stop driving the motor in reverse prior to motor damage.
After a specific time is set for the timer, the system automatically adjusts the number of clearing processes as a function of swarf characteristics so that the number of processes varies and is at least closer to the optimum number corresponding to the specific swarf characteristics. This is because heavy swarf typically results in a greater load on the motor and hence slows the reverse and forward conveyor motion. In this case any given reverse and forward clearing process takes longer when swarf is heavy than when swarf is relatively light. Therefore, given a specific clearing protocol period, the number of clearing processes corresponding to light swarf is greater than the number corresponding to light swarf.
Similarly, where swarf size is small the overall weight corresponding to a jam will likely be much greater than where swarf size is large as swarf density on the conveyor would likely be greater. Thus, the great weight of small swarf pieces would slow the clearing processes and hence a smaller number of processes would occur in a given clearing protocol time period when compared to large swarf pieces. This is the desired effect. For example, as indicated above, where swarf pieces are small it is relatively more likely that a clearing process will eliminate a jam than where swarf pieces are large. Thus, where swarf pieces are small, the number of clearing processes expected to clear a jam also small. The number of clearing processes with the present invention is related to swarf size such that small swarf naturally results in a reduced number of clearing processes and large swarf results in a greater relative number of clearing processes.
These and other objects, advantages and aspects of the invention will become apparent from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention.